Maleimide-modified high heat ABS resins

Abstract

Graft copolymerized maleimide-modified, impact resistant monovinylidene aromatic copolymer compositions have substantially improved impact strength and fatigue resistance properties when the swelling index thereof is 12 or greater and when the numerical difference in maleimide monomer content as between the grafted copolymer and matrix copolymer portions thereof differ by no more than 9 percentage points from each other. Such compositions are conveniently prepared by mass, solution or mass/suspension graft copolymerization processes and by deferring the addition of at least about 30 percent of the maleimide monomer ingredient to a point in the process after (and preferably only shortly after) phase inversion of the dissolved impact modifying rubbery polymer ingredient.

What is claimed is: 
     
       1. A rubber-modified monovinylidene aromatic copolymer composition which comprises: A. a continuous phase matrix copolymer comprising, in polymerized form and on a matrix copolymer weight basis, from about 35 to about 89 weight percent of a monovinylidene aromatic monomer, from about 10 to about 40 weight percent of an ethylenically unsaturated nitrile monomer, and from about 1 to about 25 weight percent of an N-substituted maleimide monomer; and   B. dispersed within said matrix copolymer, discrete particles of a conjugated diene homopolymer or copolymer rubber having grafted thereon and occluded therein a rigid copolymer constituent comprising, in polymerized form and on a rigid copolymer constituent weight basis, from about 25 to about 94 weight percent of a monovinylidene aromatic monomer, from about 5 to about 40 weight percent of an ethylenically unsaturated nitrile monomer, and from about 1 to about 35 weight percent of a N-substituted maleimide monomer; said rubber-modified monovinylidene aromatic copolymer composition being further characterized in that it has a swelling index value of from about 15 to about 25 and in that the difference between the N-substituted maleimide monomer content of the matrix phase copolymer and that of the grafted and occluded rigid copolymer constituent is 9 weight percentage points or less.   
     
     
       2. The aromatic copolymer composition of claim 1 wherein the N-substituted maleimide monomer of both matrix copolymer and the grafted and occluded rigid copolymer is an N-aryl maleimide. 
     
     
       3. The aromatic copolymer composition of claim 2 wherein the N-aryl maleimide is N-phenyl maleimide. 
     
     
       4. The aromatic copolymer composition of claim 3 wherein, in both the matrix copolymer and the grafted and occluded copolymer, the monovinylidene aromatic monomer is styrene and the ethylenically unsaturated nitrile is acrylonitrile. 
     
     
       5. The aromatic copolymer composition of claim 1 wherein the difference between the N-substituted maleimide content of the matrix phase and the N-substituted maleimide content of the grafted and occluded rigid copolymer is 8 weight percentage points or less. 
     
     
       6. The aromatic copolymer composition of claim 1 wherein the swelling index thereof is from about 15 to about 20. 
     
     
       7. The aromatic copolymer composition of claim 1 wherein the rubber content thereof is from about 5 to about 30 percent based upon the total weight of said composition. 
     
     
       8. The aromatic copolymer composition of claim 1 wherein said composition has been prepared by a mass, solution or mass/suspension polymerization process. 
     
     
       9. The aromatic copolymer composition of claim 8 wherein said composition further comprises, on a total composition weight basis, from about 5 to about 40 weight percent of an emulsion graft polymerized rubber concentrate which comprises, on a rubber concentrate weight basis, from about 30 to about 70 weight percent of dispersed rubber particles having grafted thereto a rigid superstrate polymer comprising, in polymerized form, a monovinylidene aromatic monomer, an ethylenically unsaturated nitrile monomer and, optionally, an N-substituted maleimide monomer.